Hydraulic roughness of biofouled pipes, biofilm character, and measured improvements from cleaning

The hydraulic performance of pipelines can be significantly affected by the presence of biological growth on internal surfaces. The change in wall roughness brought about by the biofilms has been studied by the use of headloss tests, precleaning and postcleaning of the pipelines in three Tasmanian hydroelectric schemes. Results of the headloss testing show that improvements to hydraulic efficiency can be achieved from the cleaning of biofouling material. The data, when plotted as a Moody diagram, shows that the friction law for conduits roughened by biological growths may not always follow a Colebrook-White type relationship, although the results are too narrow in Reynolds number to be conclusive. It was found that bacteria made up the majority of the biofilm biomass in the pipelines studied. Based on molecular analysis, members of the class Alphaproteobacteria were the most frequently detected followed by members of the phylum Chloroflexi.